Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Erictks on 30/05/2017 05:47:13

Title: Does a photon lose energy as it travels?
Post by: Erictks on 30/05/2017 05:47:13

Just a curious question , does a photon consume energy when it travels?

If yes, how does a photon have the energy to travel few thousand or million light years to earth ?

If they don't lose energy, how do they move?

Title: Re: Does photon lost energy ?
Post by: PmbPhy on 30/05/2017 06:10:21

Quote from: Erictks on 30/05/2017 05:47:13

Just a curious question , does photon consume energy when it travel ?

No. They don't "consume" energy.

Quote from: Erictks on 30/05/2017 05:47:13

If yes how does a photon have the energy to travel few thousand or million light years to earth ?

While photons don't consume energy as they move, the energy of a photon decreases as the result of the expansion of the universe. So after they've traveled a million light years or so they will exhibit a decrease in energy which manifest itself as a redshift.

Quote from: Erictks on 30/05/2017 05:47:13

If they don't lost the energy , how do they move ?

Nothing requires energy to move. In fact it would take energy to slow something down.

Title: Re: Does photon lost energy ?
Post by: Kryptid on 30/05/2017 23:15:02

Quote from: Erictks on 30/05/2017 05:47:13

If they don't lost the energy , how do they move ?

Newton's laws say that an object in motion will continue to move at that same speed and direction unless acted on by an outside force.

Title: Re: Does a photon lose energy as it travels?
Post by: evan_au on 31/05/2017 11:49:15

Quote from: Erictks

If they don't lose energy, how do they move?

The idea that things naturally slow down and stop all by themselves was promoted by Aristotle, who lived before 300BC. It's a natural-enough idea.

His ideas of motion were based on objects moving through air, and subject to viscosity and friction. In such an environment, it takes a continual input of energy to keep an object in horizontal motion, so he called it "unnatural motion".
See: https://en.wikipedia.org/wiki/Aristotelian_physics#Unnatural_motion

It was Galileo (around 1600AD) who started to overturn these ideas (and upset a lot of people in the process).
It was Newton who finally dispelled Aristotle's ideas of physics, with Newton's eponymous laws of motion. This said that an object will continue with a constant speed and direction unless you apply some force. But it works best in a vacuum.

Aristotle didn't really believe in a vacuum. The saying "nature abhors a vacuum" is attributed to him.
See: https://en.wikipedia.org/wiki/Horror_vacui_(physics)